Biodiversity, a portmanteau of "bio" (life) and "diversity", generally refers to the variety and variability of life on Earth. According to the United Nations Environment Programme (UNEP), biodiversity typically measures variation at the genetic, the species, and the ecosystem level.  Terrestrial biodiversity tends to be greater near the equator, [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10821282]] which seems to be the result of the warm climate and high primary productivity.  Biodiversity is not distributed evenly on Earth, and is richest in the tropics. These tropical forest ecosystems cover less than 10 per cent of earth's surface, and contain about 90 percent of the world's species. Marine biodiversity tends to be highest along coasts in the Western Pacific, where sea surface temperature is highest and in the mid-latitudinal band in all oceans. There are latitudinal gradients in species diversity. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/20668450]] Biodiversity generally tends to cluster in hotspots, [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10706275]] and has been increasing through time,  [[CITE|undefined|http://strata.geology.wisc.edu/jack]] but will be likely to slow in the future. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/19558515]]
Rapid environmental changes typically cause mass extinctions.   More than 99.9 percent of all species that ever lived on Earth, amounting to over five billion species, are estimated to be extinct.  Estimates on the number of Earth's current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described.  More recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described. [[CITE|undefined|http://nsf.gov/news/news_summ.jsp?cntn_id=138446]] The total amount of related DNA base pairs on Earth is estimated at 5.0 x 10 37 and weighs 50 billion tonnes. In comparison, the total mass of the biosphere has been estimated to be as much as 4 TtC (trillion tons of carbon). [[CITE|undefined|http://agci.org/classroom/biosphere/index.php]] In July 2016, scientists reported identifying a set of 355 genes from the Last Universal Common Ancestor (LUCA) of all organisms living on Earth.
The age of the Earth is about 4.54 billion years. [[CITE|undefined|https://web.archive.org/web/20051223072700/http://pubs.usgs.gov/gip/geotime/age.html]] [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10821282]] [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10821282]] The earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago, [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10821282]] [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10821282]] during the Eoarchean Era after a geological crust started to solidify following the earlier molten Hadean Eon. There are microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia. [[CITE|undefined|http://apnews.excite.com/article/20131113/DAA1VSC01.html]] [[CITE|undefined|http://telegraph.co.uk/news/science/science-news/10445788/Oldest-signs-of-life-on-Earth-found.html]] [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/24205812]] Other early physical evidence of a biogenic substance is graphite in 3.7 billion-year-old meta-sedimentary rocks discovered in Western Greenland.  More recently, in 2015, "remains of biotic life" were found in 4.1 billion-year-old rocks in Western Australia. [[CITE|undefined|http://apnews.excite.com/article/20151019/us-sci--earliest_life-a400435d0d.html]]  According to one of the researchers, "If life arose relatively quickly on Earth.. then it could be common in the universe." [[CITE|undefined|http://apnews.excite.com/article/20151019/us-sci--earliest_life-a400435d0d.html]]
Since life began on Earth, five major mass extinctions and several minor events have led to large and sudden drops in biodiversity. The Phanerozoic eon (the last 540 million years) marked a rapid growth in biodiversity via the Cambrian explosion —a period during which the majority of multicellular phyla first appeared.  The next 400 million years included repeated, massive biodiversity losses classified as mass extinction events. In the Carboniferous, rainforest collapse led to a great loss of plant and animal life.  The Permian–Triassic extinction event, 251 million years ago, was the worst; vertebrate recovery took 30 million years. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/18198148]] The most recent, the Cretaceous–Paleogene extinction event, occurred 65 million years ago and has often attracted more attention than others because it resulted in the extinction of the dinosaurs. 
The period since the emergence of humans has displayed an ongoing biodiversity reduction and an accompanying loss of genetic diversity. Named the Holocene extinction, the reduction is caused primarily by human impacts, particularly habitat destruction.  Conversely, biodiversity positively impacts human health in a number of ways, although a few negative effects are studied.
The United Nations designated 2011–2020 as the United Nations Decade on Biodiversity. [[CITE|undefined|http://unesco.org/new/en/natural-sciences/special-themes/biodiversity/international-day-for-biological-diversity/united-nations-decade-on-biodiversity]]
The term biological diversity was used first by wildlife scientist and conservationist Raymond F. Dasmann in the year 1968 lay book A Different Kind of Country advocating conservation. The term was widely adopted only after more than a decade, when in the 1980s it came into common usage in science and environmental policy. Thomas Lovejoy, in the foreword to the book Conservation Biology, introduced the term to the scientific community. Until then the term "natural diversity" was common, introduced by The Science Division of The Nature Conservancy in an important 1975 study, "The Preservation of Natural Diversity." By the early 1980s TNC's Science program and its head, Robert E. Jenkins, [[CITE|undefined|http://nature.org/aboutus/index.htm]] Lovejoy and other leading conservation scientists at the time in America advocated the use of the term "biological diversity".
The term's contracted form biodiversity may have been coined by W.G. Rosen in 1985 while planning the 1986 National Forum on Biological Diversity organized by the National Research Council (NRC). It first appeared in a publication in 1988 when sociobiologist E. O. Wilson used it as the title of the proceedings of that forum.
Since this period the term has achieved widespread use among biologists, environmentalists, political leaders and concerned citizens.
A similar term in the United States is "natural heritage." It pre-dates the others and is more accepted by the wider audience interested in conservation. Broader than biodiversity, it includes geology and landforms. [[CITE|undefined|http://mass.gov/eea/agencies/dfg/dfw/natural-heritage]]
"Biodiversity" is most commonly used to replace the more clearly defined and long established terms, species diversity and species richness. Biologists most often define biodiversity as the "totality of genes, species and ecosystems of a region". An advantage of this definition is that it seems to describe most circumstances and presents a unified view of the traditional types of biological variety previously identified:
- taxonomic diversity (usually measured at the species diversity level)
- ecological diversity often viewed from the perspective of ecosystem diversity
- morphological diversity which stems from genetic diversity and molecular diversity 
- functional diversity which is a measure of the number of functionally disparate species within a population (e.g. different feeding mechanism, different motility, predator vs prey, etc.) [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/20668450]]
This multilevel construct is consistent with Datman and Lovejoy.
One textbook's definition is "variation of life at all levels of biological organization".
Measuring diversity at one level in a group of organisms may not precisely correspond to diversity at other levels.
Biodiversity is not evenly distributed, rather it varies greatly across the globe as well as within regions.
Diversity consistently measures higher in the tropics and in other localized regions such as the Cape Floristic Region and lower in polar regions generally. Rain forests that have had wet climates for a long time, such as Yasuní National Park in Ecuador, have particularly high biodiversity. [[CITE|undefined|http://dotearth.blogs.nytimes.com/2010/01/20/a-durable-yet-vulnerable-eden-in-amazonia]] [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/20098736]]
Terrestrial biodiversity is thought to be up to 25 times greater than ocean biodiversity.
Generally, there is an increase in biodiversity from the poles to the tropics. Thus localities at lower latitudes have more species than localities at higher latitudes. This is often referred to as the latitudinal gradient in species diversity. Several ecological mechanisms may contribute to the gradient, but the ultimate factor behind many of them is the greater mean temperature at the equator compared to that of the poles.  [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10706275]] [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10706275]]
Even though terrestrial biodiversity declines from the equator to the poles, [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10706275]] some studies claim that this characteristic is unverified in aquatic ecosystems, especially in marine ecosystems. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10706275]] The latitudinal distribution of parasites does not appear to follow this rule.
In 2016, an alternative hypothesis ("the fractal biodiversity") was proposed to explain the biodiversity latitudinal gradient [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10706275]]. In this study, the species pool size and the fractal nature of ecosystems were combined to clarify some general patterns of this gradient. This hypothesis considers temperature, moisture, and net primary production (NPP) as the main variables of an ecosystem niche and as the axis of the ecological hypervolume. In this way, it is possible to build fractal hypervolumes, whose fractal dimension rises up to three moving towards the equator.
A biodiversity hotspot is a region with a high level of endemic species that has experienced great habitat loss. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10706275]] The term hotspot was introduced in 1988 by Norman Myers. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10706275]] [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10706275]] [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10706275]] While hotspots are spread all over the world, the majority are forest areas and most are located in the tropics.
Brazil's Atlantic Forest is considered one such hotspot, containing roughly 20,000 plant species, 1,350 vertebrates and millions of insects, about half of which occur nowhere else.  The island of Madagascar and India are also particularly notable. Colombia is characterized by high biodiversity, with the highest rate of species by area unit worldwide and it has the largest number of endemics (species that are not found naturally anywhere else) of any country. About 10% of the species of the Earth can be found in Colombia, including over 1,900 species of bird, more than in Europe and North America combined, Colombia has 10% of the world's mammals species, 14% of the amphibian species and 18% of the bird species of the world.  Madagascar dry deciduous forests and lowland rainforests possess a high ratio of endemism.  Since the island separated from mainland Africa 66 million years ago, many species and ecosystems have evolved independently. Indonesia's 17,000 islands cover 735,355 square miles (1,904,560 km 2 ) and contain 10% of the world's flowering plants, 12% of mammals and 17% of reptiles, amphibians and birds —along with nearly 240 million people.  Many regions of high biodiversity and/or endemism arise from specialized habitats which require unusual adaptations, for example, alpine environments in high mountains, or Northern European peat bogs.
Accurately measuring differences in biodiversity can be difficult.
Evolution and history
Biodiversity is the result of 3.5 billion years of evolution. The origin of life has not been definitely established by science, however some evidence suggests that life may already have been well-established only a few hundred million years after the formation of the Earth. Until approximately 600 million years ago, all life consisted of microorganisms – archaea, bacteria, and single-celled protozoans and protists.
The history of biodiversity during the Phanerozoic (the last 540 million years), starts with rapid growth during the Cambrian explosion —a period during which nearly every phylum of multicellular organisms first appeared. Over the next 400 million years or so, invertebrate diversity showed little overall trend and vertebrate diversity shows an overall exponential trend. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/20106856]] This dramatic rise in diversity was marked by periodic, massive losses of diversity classified as mass extinction events. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/20106856]] A significant loss occurred when rainforests collapsed in the carboniferous.  The worst was the Permian-Triassic extinction event, 251 million years ago. Vertebrates took 30 million years to recover from this event. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/18198148]]
The fossil record suggests that the last few million years featured the greatest biodiversity in history. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/20106856]] However, not all scientists support this view, since there is uncertainty as to how strongly the fossil record is biased by the greater availability and preservation of recent geologic sections. Some scientists believe that corrected for sampling artifacts, modern biodiversity may not be much different from biodiversity 300 million years ago.,  whereas others consider the fossil record reasonably reflective of the diversification of life. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/20106856]] Estimates of the present global macroscopic species diversity vary from 2 million to 100 million, with a best estimate of somewhere near 9 million, the vast majority arthropods. [[CITE|undefined|http://unep.org/ourplanet/imgversn/85/heywood.html]] Diversity appears to increase continually in the absence of natural selection. 
The existence of a "global carrying capacity", limiting the amount of life that can live at once, is debated, as is the question of whether such a limit would also cap the number of species.
It also appears that the diversity continue to increase over time, especially after mass extinctions.
On the other hand, changes through the Phanerozoic correlate much better with the hyperbolic model (widely used in population biology, demography and macrosociology, as well as fossil biodiversity) than with exponential and logistic models. The latter models imply that changes in diversity are guided by a first-order positive feedback (more ancestors, more descendants) and/or a negative feedback arising from resource limitation. Hyperbolic model implies a second-order positive feedback. The hyperbolic pattern of the world population growth arises from a second-order positive feedback between the population size and the rate of technological growth. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/18677962]] The hyperbolic character of biodiversity growth can be similarly accounted for by a feedback between diversity and community structure complexity. The similarity between the curves of biodiversity and human population probably comes from the fact that both are derived from the interference of the hyperbolic trend with cyclical and stochastic dynamics. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/18677962]] [[CITE|undefined|http://strata.geology.wisc.edu/jack]]
Most biologists agree however that the period since human emergence is part of a new mass extinction, named the Holocene extinction event, caused primarily by the impact humans are having on the environment. [[CITE|undefined|http://strata.geology.wisc.edu/jack]] It has been argued that the present rate of extinction is sufficient to eliminate most species on the planet Earth within 100 years.
With the “Biodiversity-related Niches Differentiation Theory” (BNDT) [[CITE|undefined|http://strata.geology.wisc.edu/jack]] Roberto Cazzolla Gatti recently proposed that species themselves are the architects of biodiversity, by proportionally increasing the number of potentially available niches in a given ecosystem. This study led to the idea that biodiversity is autocatalytic [[CITE|undefined|http://strata.geology.wisc.edu/jack]]. An ecosystem of interdependent species can be, therefore, considered as an emergent autocatalytic set (a self-sustaining network of mutually “catalytic” entities), where one (group of) species enables the existence of (i.e., creates niches for) other species. This view offers a possible answer to the fundamental question of why so many species can coexist in the same ecosystem.
New species are regularly discovered (on average between 5–10,000 new species each year, most of them insects) and many, though discovered, are not yet classified (estimates are that nearly 90% of all arthropods are not yet classified). [[CITE|undefined|http://unep.org/ourplanet/imgversn/85/heywood.html]] Most of the terrestrial diversity is found in tropical forests and in general, land has more species than the ocean; some 8.7 million species may exists on Earth, of which some 2.1 million live in the ocean.
"Ecosystem services are the suite of benefits that ecosystems provide to humanity."
These services come in three flavors:
There have been many claims about biodiversity's effect on these ecosystem services, especially provisioning and regulating services.
- Greater species diversity of plants increases fodder yield (synthesis of 271 experimental studies).
- Greater genetic diversity of plants (i.e.: diversity within a single species) increases overall crop yield (synthesis of 575 experimental studies).
- Greater species diversity of trees increases overall wood production (Synthesis of 53 experimental studies).
- Greater species diversity of fish increases the stability of fisheries yield (Synthesis of 8 observational studies) [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/22678280]]
- Greater species diversity of natural pest enemies decreases herbivorous pest populations (Data from two separate reviews; Synthesis of 266 experimental and observational studies; Synthesis of 18 observational studies.
- Greater species diversity of plants decreases disease prevalence on plants (Synthesis of 107 experimental studies) 
- Greater species diversity of plants increases resistance to plant invasion (Data from two separate reviews; Synthesis of 105 experimental studies;  Synthesis of 15 experimental studies )
- Greater species diversity of plants increases carbon sequestration, but note that this finding only relates to actual uptake of carbon dioxide and not long term storage, see below; Synthesis of 479 experimental studies) [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/21613148]]
- Greater species diversity of plants increases soil nutrient remineralization (Synthesis of 103 experimental studies) 
- Greater species diversity of plants increases soil organic matter (Synthesis of 85 experimental studies) 
- None to date
- Greater species diversity of plants may or may not decrease herbivorous pest populations.
- Greater species diversity of animals may or may not decrease disease prevalence on those animals (Synthesis of 45 experimental and observational studies), [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/21124449]] although a 2013 study offers more support showing that biodiversity may in fact enhance disease resistance within animal communities, at least in amphibian frog ponds.
- Greater species and trait diversity of plants may or may not increase long term carbon storage (Synthesis of 33 observational studies) [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/22678280]]
- Greater pollinator diversity may or may not increase pollination (Synthesis of 7 observational studies), [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/22678280]] but a publication from March 2013 suggests that increased native pollinator diversity enhances pollen deposition (although not necessarily fruit set as the authors would have you believe, for details explore their lengthy supplementary material).
- Greater species diversity of plants reduces primary production (Synthesis of 7 experimental studies) [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/21613148]]
- Greater genetic and species diversity of a number of organisms reduces freshwater purification (Synthesis of 8 experimental studies, although an attempt by the authors to investigate the effect of detritivore diversity on freshwater purification was unsuccessful due to a lack of available evidence (only 1 observational study was found [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/22678280]]
- Effect of species diversity of plants on biofuel yield (In a survey of the literature, the investigators only found 3 studies) [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/22678280]]
- Effect of species diversity of fish on fishery yield (In a survey of the literature, the investigators only found 4 experimental studies and 1 observational study) [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/22678280]]
- Effect of species diversity on the stability of biofuel yield (In a survey of the literature, the investigators did not find any studies) [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/22678280]]
- Effect of species diversity of plants on the stability of fodder yield (In a survey of the literature, the investigators only found 2 studies) [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/22678280]]
- Effect of species diversity of plants on the stability of crop yield (In a survey of the literature, the investigators only found 1 study) [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/22678280]]
- Effect of genetic diversity of plants on the stability of crop yield (In a survey of the literature, the investigators only found 2 studies) [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/22678280]]
- Effect of diversity on the stability of wood production (In a survey of the literature, the investigators could not find any studies) [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/22678280]]
- Effect of species diversity of multiple taxa on erosion control (In a survey of the literature, the investigators could not find any studies – they did however find studies on the effect of species diversity and root biomass) [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/22678280]]
- Effect of diversity on flood regulation (In a survey of the literature, the investigators could not find any studies) [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/22678280]]
- Effect of species and trait diversity of plants on soil moisture (In a survey of the literature, the investigators only found 2 studies) [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/22678280]]
Other sources have reported somewhat conflicting results and in 1997 Robert Costanza and colleagues reported the estimated global value of ecosystem services (not captured in traditional markets) at an average of $33 trillion annually.
Since the stone age, species loss has accelerated above the average basal rate, driven by human activity. Estimates of species losses are at a rate 100-10,000 times as fast as is typical in the fossil record. Biodiversity also affords many non-material benefits including spiritual and aesthetic values, knowledge systems and education.
Agricultural diversity can be divided into two categories: intraspecific diversity, which includes the genetic variety within a single species, like the potato (Solanum tuberosum ) that is composed of many different forms and types (e.g.: in the U.S. we might compare russet potatoes with new potatoes or purple potatoes, all different, but all part of the same species, S. tuberosum).
The other category of agricultural diversity is called interspecific diversity and refers to the number and types of different species. Thinking about this diversity we might note that many small vegetable farmers grow many different crops like potatoes and also carrots, peppers, lettuce etc.
Agricultural diversity can also be divided by whether it is ‘planned’ diversity or ‘associated’ diversity.
The control of associated biodiversity is one of the great agricultural challenges that farmers face.
Interspecific crop diversity is, in part, responsible for offering variety in what we eat.
- The Irish potato blight of 1846 was a major factor in the deaths of one million people and the emigration of about two million. It was the result of planting only two potato varieties, both vulnerable to the blight, Phytophthora infestans
- When rice grassy stunt virus struck rice fields from Indonesia to India in the 1970s, 6,273 varieties were tested for resistance. [[CITE|undefined|http://lumrix.net/health/Rice_grassy_stunt_virus.html]] Only one was resistant, an Indian variety and known to science only since 1966. [[CITE|undefined|http://lumrix.net/health/Rice_grassy_stunt_virus.html]] This variety formed a hybrid with other varieties and is now widely grown. [[CITE|undefined|http://lumrix.net/health/Rice_grassy_stunt_virus.html]]
- Coffee rust attacked coffee plantations in Sri Lanka, Brazil and Central America in 1970. A resistant variety was found in Ethiopia. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/6694743]] The diseases are themselves a form of biodiversity.
Monoculture was a contributing factor to several agricultural disasters, including the European wine industry collapse in the late 19th century and the US southern corn leaf blight epidemic of 1970. 
Although about 80 percent of humans' food supply comes from just 20 kinds of plants,  humans use at least 40,000 species.
Biodiversity's relevance to human health is becoming an international political issue, as scientific evidence builds on the global health implications of biodiversity loss.
The growing demand and lack of drinkable water on the planet presents an additional challenge to the future of human health.
Some of the health issues influenced by biodiversity include dietary health and nutrition security, infectious disease, medical science and medicinal resources, social and psychological health.
Biodiversity provides critical support for drug discovery and the availability of medicinal resources.
Many industrial materials derive directly from biological sources.
Biodiversity enriches leisure activities such as hiking, birdwatching or natural history study. Biodiversity inspires musicians, painters, sculptors, writers and other artists. Many cultures view themselves as an integral part of the natural world which requires them to respect other living organisms.
Popular activities such as gardening, fishkeeping and specimen collecting strongly depend on biodiversity. The number of species involved in such pursuits is in the tens of thousands, though the majority do not enter commerce.
The relationships between the original natural areas of these often exotic animals and plants and commercial collectors, suppliers, breeders, propagators and those who promote their understanding and enjoyment are complex and poorly understood.
Philosophically it could be argued that biodiversity has intrinsic aesthetic and spiritual value to mankind in and of itself. This idea can be used as a counterweight to the notion that tropical forests and other ecological realms are only worthy of conservation because of the services they provide. 
Biodiversity supports many ecosystem services :
It plays a part in regulating the chemistry of our atmosphere and water supply. Biodiversity is directly involved in water purification, recycling nutrients and providing fertile soils. Experiments with controlled environments have shown that humans cannot easily build ecosystems to support human needs; for example insect pollination cannot be mimicked, and that activity alone represented between $2.1-14.6 billions in 2003. [[CITE|-1|http://doi.org/10.1641/0006-3568(2006)56[311:TEVOES]2.0.CO;2]]
Number of species
According to Mora and colleagues, the total number of terrestrial species is estimated to be around 8.7 million while the number of oceanic species is much lower, estimated at 2.2 million.
- 220,000 vascular plants, estimated using the species-area relation method 
- 0.7-1 million marine species 
- 10–30 million insects; [[CITE|undefined|http://si.edu/Encyclopedia_SI/nmnh/buginfo/bugnos.htm]] (of some 0.9 million we know today) [[CITE|undefined|http://lemonde.fr/planete/article/2006/06/27/protection-de-la-biodiversite-un-inventaire-difficile_788741_3244.html]]
- 5–10 million bacteria; [[CITE|undefined|http://news.bbc.co.uk/2/hi/science/nature/5232928.stm]]
- 1.5-3 million fungi, estimates based on data from the tropics, long-term non-tropical sites and molecular studies that have revealed cryptic speciation.  Some 0.075 million species of fungi had been documented by 2001) 
- 1 million mites [[CITE|undefined|http://insects.ummz.lsa.umich.edu/ACARI/index.html]]
- The number of microbial species is not reliably known, but the Global Ocean Sampling Expedition dramatically increased the estimates of genetic diversity by identifying an enormous number of new genes from near-surface plankton samples at various marine locations, initially over the 2004-2006 period.  The findings may eventually cause a significant change in the way science defines species and other taxonomic categories. [[CITE|undefined|http://scientificamerican.com/podcast/episode.cfm?id=74F46951-E7F2-99DF-37873C5B678DC19D]] [[CITE|undefined|http://ploscollections.org/article/browseIssue.action?issue=info%3Adoi%2F10.1371%2Fissue.pcol.v06.i02]]
Since the rate of extinction has increased, many extant species may become extinct before they are described.
Species loss rates
During the last century, decreases in biodiversity have been increasingly observed.
In absolute terms, the planet has lost 52% of its biodiversity since 1970 according to a 2014 study by the World Wildlife Fund. The Living Planet Report 2014 claims that "the number of mammals, birds, reptiles, amphibians and fish across the globe is, on average, about half the size it was 40 years ago". Of that number, 39% accounts for the terrestrial wildlife gone, 39% for the marine wildlife gone and 76% for the freshwater wildlife gone. Biodiversity took the biggest hit in Latin America, plummeting 83 percent. High-income countries showed a 10% increase in biodiversity, which was canceled out by a loss in low-income countries. This is despite the fact that high-income countries use five times the ecological resources of low-income countries, which was explained as a result of process whereby wealthy nations are outsourcing resource depletion to poorer nations, which are suffering the greatest ecosystem losses. [[CITE|undefined|http://assets.worldwildlife.org/publications/723/files/original/LPR2014_low_res-2.pdf?1412025775=]]
A 2017 study published in PLOS One found that the biomass of insect life in Germany had declined by three-quarters in the last 25 years. Dave Goulson of Sussex University stated that their study suggested that humans "appear to be making vast tracts of land inhospitable to most forms of life, and are currently on course for ecological Armageddon. If we lose the insects then everything is going to collapse." [[CITE|undefined|https://theguardian.com/environment/2017/oct/18/warning-of-ecological-armageddon-after-dramatic-plunge-in-insect-numbers]]
In 2006 many species were formally classified as rare or endangered or threatened; moreover, scientists have estimated that millions more species are at risk which have not been formally recognized. About 40 percent of the 40,177 species assessed using the IUCN Red List criteria are now listed as threatened with extinction —a total of 16,119. [[CITE|undefined|http://news.nationalgeographic.com/news/2006/05/0502_060502_endangered.html]]
Jared Diamond describes an "Evil Quartet" of habitat destruction, overkill, introduced species and secondary extinctions. Edward O. Wilson prefers the acronym HIPPO, standing for H abitat destruction, I nvasive species, P ollution, human over-Population and O ver-harvesting. The most authoritative classification in use today is IUCN's Classification of Direct Threats [[CITE|undefined|http://conservationmeasures.org/initiatives/threats-actions-taxonomies/threats-taxonomy]] which has been adopted by major international conservation organizations such as the US Nature Conservancy, the World Wildlife Fund, Conservation International and BirdLife International.
Habitat destruction has played a key role in extinctions, especially related to tropical forest destruction. Factors contributing to habitat loss are: overconsumption, overpopulation, land use change, deforestation, [[CITE|undefined|http://eoearth.org/article/Deforestation]] pollution (air pollution, water pollution, soil contamination) and global warming or climate change.
Habitat size and numbers of species are systematically related.
A 2007 study conducted by the National Science Foundation found that biodiversity and genetic diversity are codependent—that diversity among species requires diversity within a species and vice versa. "If any one type is removed from the system, the cycle can break down and the community becomes dominated by a single species."  At present, the most threatened ecosystems are found in fresh water, according to the Millennium Ecosystem Assessment 2005, which was confirmed by the "Freshwater Animal Diversity Assessment", organised by the biodiversity platform and the French Institut de recherche pour le développement (MNHNP). [[CITE|undefined|http://scienceconnection.be]]
Co-extinctions are a form of habitat destruction.
Barriers such as large rivers, seas, oceans, mountains and deserts encourage diversity by enabling independent evolution on either side of the barrier, via the process of allopatric speciation. The term invasive species is applied to species that breach the natural barriers that would normally keep them constrained. Without barriers, such species occupy new territory, often supplanting native species by occupying their niches, or by using resources that would normally sustain native species.
The number of species invasions has been on the rise at least since the beginning of the 1900s.
Not all introduced species are invasive, nor all invasive species deliberately introduced.
Finally, an introduced species may unintentionally injure a species that depends on the species it replaces.
At present, several countries have already imported so many exotic species, particularly agricultural and ornamental plants, that their own indigenous fauna/flora may be outnumbered.
Endemic species can be threatened with extinction  through the process of genetic pollution, i.e. uncontrolled hybridization, introgression and genetic swamping. Genetic pollution leads to homogenization or replacement of local genomes as a result of either a numerical and/or fitness advantage of an introduced species. [[CITE|undefined|http://nativeseednetwork.org/article_view?id=13]] Hybridization and introgression are side-effects of introduction and invasion. These phenomena can be especially detrimental to rare species that come into contact with more abundant ones. The abundant species can interbreed with the rare species, swamping its gene pool. This problem is not always apparent from morphological (outward appearance) observations alone. Some degree of gene flow is normal adaptation and not all gene and genotype constellations can be preserved. However, hybridization with or without introgression may, nevertheless, threaten a rare species' existence. [[CITE|undefined|http://jstor.org/stable/2097230]]
Overexploitation occurs when a resource is consumed at an unsustainable rate.
The overkill hypothesis, a pattern of large animal extinctions connected with human migration patterns, can be used explain why megafaunal extinctions can occur within a relatively short time period. 
In agriculture and animal husbandry, the Green Revolution popularized the use of conventional hybridization to increase yield. Often hybridized breeds originated in developed countries and were further hybridized with local varieties in the developing world to create high yield strains resistant to local climate and diseases. Local governments and industry have been pushing hybridization. Formerly huge gene pools of various wild and indigenous breeds have collapsed causing widespread genetic erosion and genetic pollution. This has resulted in loss of genetic diversity and biodiversity as a whole. [[CITE|undefined|https://web.archive.org/web/20090518120050/http://www.farmedia.org/bulletins/bulletin28.html]]
Genetically modified organisms contain genetic material that is altered through genetic engineering. Genetically modified crops have become a common source for genetic pollution in not only wild varieties, but also in domesticated varieties derived from classical hybridization.  [[CITE|undefined|http://iufro-archive.boku.ac.at/silvavoc/glossary/6_0en.html]] [[CITE|undefined|http://www.scienzagiovane.unibo.it/English/pollution/2-facets.html]]
Genetic erosion and genetic pollution have the potential to destroy unique genotypes, threatening future access to food security. A decrease in genetic diversity weakens the ability of crops and livestock to be hybridized to resist disease and survive changes in climate. [[CITE|undefined|https://web.archive.org/web/20090518120050/http://www.farmedia.org/bulletins/bulletin28.html]]
Global warming is also considered to be a major potential threat to global biodiversity in the future.
Climate change has seen many claims about potential to affect biodiversity but evidence supporting the statement is tenuous.
In 2004, an international collaborative study on four continents estimated that 10 percent of species would become extinct by 2050 because of global warming.
A recent study predicts that up to 35% of the world terrestrial carnivores and ungulates will be at higher risk of extinction by 2050 because of the joint effects of predicted climate and land-use change under business-as-usual human development scenarios.
From 1950 to 2011, world population increased from 2.5 billion to 7 billion and is forecast to reach a plateau of more than 9 billion during the 21st century.
According to a 2014 study by the World Wildlife Fund, the global human population already exceeds planet's biocapacity- it would take the equivalent of 1.5 Earths of biocapacity to meet our current demands. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10821282]] The report further points that if everyone on the planet had the Footprint of the average resident of Qatar, we would need 4.8 Earths and if we lived the lifestyle of a typical resident of the USA, we would need 3.9 Earths. [[CITE|undefined|http://assets.worldwildlife.org/publications/723/files/original/LPR2014_low_res-2.pdf?1412025775=]]
The Holocene extinction
Rates of decline in biodiversity in this sixth mass extinction match or exceed rates of loss in the five previous mass extinction events in the fossil record. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10821282]] [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/18695221]] [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10821282]] [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10821282]] [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10821282]] [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10821282]] [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10821282]] Loss of biodiversity results in the loss of natural capital that supplies ecosystem goods and services. From the perspective of the method known as Natural Economy the economic value of 17 ecosystem services for Earth's biosphere (calculated in 1997) has an estimated value of US$33 trillion (3.3x10 13 ) per year. [[CITE|undefined|https://web.archive.org/web/20091226124242/http://www.uvm.edu/giee/publications/Nature_Paper.pdf]]
Conservation biology matured in the mid-20th century as ecologists, naturalists and other scientists began to research and address issues pertaining to global biodiversity declines. [[CITE|undefined|http://jstor.org/stable/1310054]]
The conservation ethic advocates management of natural resources for the purpose of sustaining biodiversity in species, ecosystems, the evolutionary process and human culture and society. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/18695221]] [[CITE|undefined|http://jstor.org/stable/1310054]] [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10821282]]
Conservation biology is reforming around strategic plans to protect biodiversity.
In the EU Directive 1999/22/EC zoos are described as having a role in the preservation of the biodiversity of wildlife animals by conducting research or participation in breeding programs. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10821282]]
Removal of exotic species will allow the species that they have negatively impacted to recover their ecological niches.
As sustainable populations of the remaining native species in an area become assured, "missing" species that are candidates for reintroduction can be identified using databases such as the Encyclopedia of Life and the Global Biodiversity Information Facility.
- Biodiversity banking places a monetary value on biodiversity. One example is the Australian Native Vegetation Management Framework.
- Gene banks are collections of specimens and genetic material. Some banks intend to reintroduce banked species to the ecosystem (e.g., via tree nurseries). [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10821282]]
- Reduction of and better targeting of pesticides allows more species to survive in agricultural and urbanized areas.
- Location-specific approaches may be less useful for protecting migratory species.
Protected areas is meant for affording protection to wild animals and their habitat which also includes forest reserves and biosphere reserves.
National park and nature reserve is the area selected by governments or private organizations for special protection against damage or degradation with the objective of biodiversity and landscape conservation.
Wildlife sanctuary aims only at conservation of species and have the following features:
The forests play a vital role in harbouring more than 45,000 floral and 81,000 faunal species of which 5150 floral and 1837 faunal species are endemic.
In zoological parks or zoos, live animals are kept for public recreation, education and conservation purposes.
Botanical garden is a garden in which plants are grown and displayed primarily for scientific and educational purposes.
Focusing on limited areas of higher potential biodiversity promises greater immediate return on investment than spreading resources evenly or focusing on areas of little diversity but greater interest in biodiversity.
A second strategy focuses on areas that retain most of their original diversity, which typically require little or no restoration.
- United Nations Convention on Biological Diversity (1992) and Cartagena Protocol on Biosafety;
- Convention on International Trade in Endangered Species (CITES);
- Ramsar Convention (Wetlands);
- Bonn Convention on Migratory Species;
- World Heritage Convention (indirectly by protecting biodiversity habitats)
- Regional Conventions such as the Apia Convention
- Bilateral agreements such as the Japan-Australia Migratory Bird Agreement.
Global agreements such as the Convention on Biological Diversity, give "sovereign national rights over biological resources" (not property). The agreements commit countries to "conserve biodiversity", "develop resources for sustainability" and "share the benefits" resulting from their use. Biodiverse countries that allow bioprospecting or collection of natural products, expect a share of the benefits rather than allowing the individual or institution that discovers/exploits the resource to capture them privately. Bioprospecting can become a type of biopiracy when such principles are not respected.
Sovereignty principles can rely upon what is better known as Access and Benefit Sharing Agreements (ABAs). The Convention on Biodiversity implies informed consent between the source country and the collector, to establish which resource will be used and for what and to settle on a fair agreement on benefit sharing.
Biodiversity is taken into account in some political and judicial decisions:
- The relationship between law and ecosystems is very ancient and has consequences for biodiversity.
- Law regarding species is more recent.
- Laws regarding gene pools are only about a century old.
Uniform approval for use of biodiversity as a legal standard has not been achieved, however.
India passed the Biological Diversity Act in 2002 for the conservation of biological diversity in India.
Less than 1% of all species that have been described have been studied beyond simply noting their existence.
Diversity study (botany)
The number of morphological attributes that can be scored for diversity study is generally limited and prone to environmental influences; thereby reducing the fine resolution required to ascertain the phylogenetic relationships.
In the case of cowpea, a study conducted to assess the level of genetic diversity in cowpea germplasm and related wide species, where the relatedness among various taxa were compared, primers useful for classification of taxa identified, and the origin and phylogeny of cultivated cowpea classified show that SSR markers are useful in validating with species classification and revealing the center of diversity. [[CITE|undefined|http://www.ncbi.nlm.nih.gov/pubmed/10821282]]